5 Application of Information
5.1 The replacement of fittings
5.1.1 Maintenance cost and Equipment Age
Typically the accepted life of a streetlight luminaire as quoted by the manufacturers is between 15 and 20 years. However, a luminaire is a fairly simple device and if the body of the fitting is sound it can be kept functional almost indefinitely by replacing three to four items. This is typically what is happening in South Africa, there are numerous fittings installed that are well over 40 years old which are still operational.
Older fittings however are often of poor design (in terms of lumen and thermal efficiency) the reflectors have become non-reflective and the diffusers badly discoloured. This has the result of decreasing the lamp life and also increasing the probability of repeat failures, which ultimately increases the maintenance costs on these fittings. It is necessary to determine what the impact of fitting age on maintenance cost is, and what the ideal replacement cycle is.
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The Benoni database does not distinguish between the manufacturer and age of the fittings to allow the calculation and apportionment of these increased costs; however the database allows some comparisons to be made in terms of areas (or even streets). By careful selection of these areas a comparison can be made between various fittings of known installation date.
Three sample areas of approximately 250 fittings each were selected from the database, the age of the areas (according to installation date) is 4, 12 and 18 years. The data yielded the following results.
Table 5-1: Quantification of Faults vs. Fitting Age
Number of Fittings No of Faults Percentage Faults To Total fittings Poles with Faults Percentage Lamp Faults
to Total fittings Percentage Repeat Faults to Failed fittings
4 year area (14 Months data)
251 70 27.80%
66 23.50%
5.71%
12 veararea (14 Months)
264 96 36.36%
74 28.03%
22.92%
18 veararea (14 months)
236 103 43.64%
66 27.97%
35.92%
A B C = B/A
D
E
=(B-D)/D
An additional comparison of the types of faults between the different sample areas can also be made, the results are as follows
Table 5-2: Contribution by Subcategory of Faults to Fittings of Differing Age
Fault Sub Cateaorv Pole
Contactor Daylight Switch Ballast
Capacitor Diffuser Ignitor Lamp Lamp Holder Fuse/Circuit Breaker New Fitting
Other Total
4 vear area 2.50%
—
~
—
— 3.00%
— 81.70%
1.40%
11.40%
~
~ 100.00%
12 veararea 1.90%
0.00%
2.40%
2.20%
0.60%
4.00%
0.15%
69.10%
1.20%
7.80%
4.80%
5.85%
100.00%
18 veararea 1.81%
0.20%
2.40%
3.70%
1.51%
3.20%
0.20%
65.10%
2.10%
6.20%
6.60%
6.98%
100.00%
Percent Total Network
1.84%
0.06%
1.96%
3.69%
1.41%
3.10%
0.20%
65.11%
1.92%
6.82%
6.40%
7.49%
100.00%
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The latter comparison clearly indicates that most maintenance costs on new fittings are lamp related. In the older fittings other factors also contribute to the maintenance costs although lamp replacement is still the dominant cost driver.
To calculate the difference in maintenance costs for the sample areas the material and labour costs can be determined using market related prices for each of the identified faults. The resultant costs are as follows:
Table 5-3: Maintenance Cost by Fitting Age
Cost Tvpe Luminaire Aqe
Fixed overhead costs Management
Faults common to old and new luminaires
Total' Fixed Cost' Age dependant luminaire maintenance cost
Total Maintenance costs
Rand value per fittinq per month 0
Years R3.50 R3.50 R2.75 R9.75 R0.00 R9.75
2 Years
R3.50 R3.50 R2.75 R9.75 R0.50 R 10.25
4 Years
R3.50 R3.50 R2.75 R9.75 R 1.00 R 10.75
12
Years R3.50 R3.50 R2.75 R9.75 R 1.48 R 11.23
18 Years
R3.50 R3.50 R2.75 R9.75 R2.92 R 12.67
Plotting the abovementioned points in graphical format produces the following results.
Figure 5-1: Average Maintenance Cost vs. Age - Benoni
This figure shows the rise in costs as fittings age
i
!
R 25.00 -
R 15.00 -
R 10.00 ;
R 5.00 •
| ^ H Variable Costs H H Fixed Cost ••••*•••• Data Points |
. . . . .. ^ ,_^—*—-—~"*
•
Age (years)
0 4
r ^
a
I I I 111
"*
To find the optimum replacement cycle the variable maintenance costs and an average new fitting cost of R500.00 have been used to calculate the annual
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equivalent annuity (AEA) of various cycle times. The relevant calculations are shown in Annexure E, the results are as follows:
Table 5-4: Calculation of Optimum Fitting Replacement Cycle - Age Related costs Cycle
Time Years 15 16 17 18 19 20 21 22 23 24 25 30 35
PVof Maintenance
R 162.80 R 178.27 R 194.32 R 210.98 R 228.28 R 246.23 R 264.87 R 284.23 R 304.31 R 325.17 R 346.81 R 468.07 R 614.24
Purchase price of
new fitting R 500.00 R 500.00 R500.00 R 500.00 R 500.00 R 500.00 R 500.00 R 500.00 R 500.00 R 500.00 R 500.00 R 500.00 R 500.00
PV R 662.80 R 678.27 R 694.32 R 710.98 R 728.28 R 746.23 R 764.87 R 784.23 R 804.31 R 825.17 R 846.81 R 968.07 R 1,114.24
(5%) Annuity
Factor 10.3797 10.8378 11.2741 11.6896 12.0853 12.4622 12.8212 13.1630 13.4886 13.7986 14.0939 15.3725 16.3742
Annual Equivalent
Annuity R61.53 R 60.11 R 58.99 R 58.14 R 57.52 R 57.11 R 56.88 R 56.84 R 56.95 R 57.23 R 57.65 R61.91 R 69.86
The calculations above indicate that a replacement cycle of 22 years is optimal, there is however only a small cost difference between the 20, 21 and 22 year cycles. The effect of an increase in the discount rate used would result in a lengthening of the replacement cycle and visa versa.
The National Treasury departments PPP unit utilises a money discount rate for LA's of between 10 and 12% per annum, if the real discount rate of 5% is combined with an anticipated inflation rate of 6% an equivalent money discount rate of 11.3% is achieved. For this reason a real discount rate of 5% per annum has been used in all the AEA calculations as this eliminates the need to 'estimate' the inflation rate.
By increasing the number of points and introducing additional sample areas the accuracy of the figures and trend line can be improved. However, given the time frames required to accumulate usable data and the lack of accurate records/inventory available in SA it is unlikely that these figures can be improved on at the present moment.
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5.1.2 Energy Savings
As detailed there are energy savings which can be introduced through the use of energy efficient light sources, in South Africa the High Pressure Sodium (HPS) Lamps have become the technology of choice in energy efficient installations even though Low Pressure Sodium lamps are more energy efficient. This is due to the shorter life span and high lamp costs of LPS lamps and the relatively low energy charges in S.A. In Europe, there is prevalent use of Low pressure sodium (LPS) lamps, mainly as a result of the higher energy charges in these countries.
The objective is to determine at what stage the introduction of energy efficient lighting is optimal. To calculate this one needs to evaluate the total lifecycle costs of a particular luminaire. These costs however depend on the chosen maintenance strategy and regular maintenance costs. The two major strategies that can be followed are as follows;
• Burn to extinction (B-T-E)
• Group Replacement (Bulk)
With a B-T-E strategy it is difficult to compare life cycle cost between Mercury Vapour and HPS lamps, due largely to the fact that MV lamps can burn for many years (albeit at a greatly reduced output) i.e. no defined end of life, whereas the HPS lamps fail completely at the end of life. Leaving MV lamps to burn long after the light output has become unacceptable is common practice in this country, which makes cost comparison almost impossible between the two technologies. In order to compare the costs one must assume that MV lamps are replaced after their output has dropped below an acceptable level.
Further complicating the issue is the differing life expectancy of different HPS lamps (average life varies from 12000 to 24000 hours depending on manufacturer and specification). The procurement policy of most LA's is such that the lowest cost item is usually purchased with little regard to quality and expected life, this results in a myriad of different types of lamps installed which, makes accurate analysis extremely difficult.
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A preliminary comparison can be made by assuming a replacement cycle of 16000 operating hours (± four years) for both HPS and Mercury Vapour lamps.
The following additional assumptions are used in the calculations presented below:
• Energy costs of 16c/kWh
• Burning hours per annum 4000
• Lamp Replacement cycle 16000 hours for both MV and HPS
• Fittings Compared
o 125 W Mercury Vapour - output 6500 lumen o 70 W HPS-output 6300 lumen
• Lamp Costs R15 for MV and R47.50 for HPS
• Luminaire Replacement Cycle - 20 Years
• A 'real' discount rate of 5%
Table 5-5: Life Cycle Costs of 125W MV vs. 70W HPS Life Cycle Cost Comparison Capital Cost
Energy Costs Lamp Costs
Undiscounted Total Costs
Present Value @ 5% 'Real' discount rate
125WMV R 445.00 R 1,792.00
R 75.00 R 2,312.00 R 1,604.98
70W HPS R 470.50 R 1,075.20
R 237.50 R 1,783.20 R 1,277.81
Figure 5-2: Life Cycle Cost of 125W MV vs. 70W HPS Fitting
R 2,500.00 R 2,000.00 R 1,500.00 R 1,000.00 R 500.00
R0.00
125WMV 70WHPS Fitting Type
• Lamp Costs
• Energy Costs
• Capital Cost
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The above shows that the 125W MV is clearly more expensive than the 70W HPS over a 20 year lifecycle.
Based on the above the replacement approach for fittings older than 20 years is obviously to replace the MV fitting with an HPS fitting. However where the MV fittings are less than 20 years old we need to determine the optimal age for converting to energy efficient technology.
To calculate the optimum replacement cycle a comparison is made between a number of cycles i.e. where the HPS fitting is introduced at various times. Note:
an age-related replacement cycle of 20 years has been adopted from 5.1.1 above. The relevant calculations are shown in Annexure F, the results are as follows:
Table 5-6: Optimum Replacement Cycle for conversion to Energy Efficient Luminaire
Replacement Strategy Immediate Replacement Replacement after 1 Year Replacement after 5 Years Replacement after 10 Years Replacement after 15 Years Replacement after 20 Years
Cycle Time Years 20 21 25 30 35 40
PV R 1,277.81 R 1,302.29 R 1,401.46 R 1,498.82 R 1,575.51 R 1,618.64
(5%) Annuity Factor 12.4622 12.8212 14.0939 15.3725 16.3742 17.1591
Annual Equivalent Annuity R 102.53 R 101.57 R 99.44 R 97.50 R 96.22 R 94.33
The interpretation of the above is that existing 125W MV luminaires should be allowed to run to the end of their useful life (20 - 22 Years) before being replaced, at that stage they should be replaced with the most efficient technology available (in terms of total life cycle cost). This optimum cycle can be shown to be different for higher rated luminaires (i.e. 250W MV) where the optimal introduction of energy efficient fittings is after about 17 years.